The present invention relates to a method of avoiding localized hydrogen build-ups in the atmosphere of safety tanks of reactors, especially light water reactors.
After a breakdown or the like that is accompanied by the loss of coolant, hydrogen forms in the core primarily due to radiolysis. The hydrogen escapes at the break or rupture in the primary circuit, and mixes with the oxygen-containing atmosphere. Consequently, ignitable hydrogen/oxygen mixtures can result in localized regions of the safety tank, for example in the vicinity of the break.
In order when breakdown of the coolant flow occurs to be able to break up or dissipate such ignitable hydrogen build-ups, it is known to disturb the density equilibrium in such localized atmospheres that are disposed in superimposed layers in the safety tank. In particular, the atmospheres are disturbed by providing within or externally of the safety tank circulating fans and/or recombinators that by means of forced air flows intermix the different atmosphere layers that are in equilibrium with one another, and thereby break up localize d hydrogen build-ups. Unfortunately, these known methods are relatively complex and expensive since they require large fans that have their own supply of power and for which special measures must in addition be provided to protect against breakdown.
Pursuant to another known method (DE-OS 28 05 476), the drawbacks associated with the use of fans and/or recombinators, where the free hydrogen is oxidized, for example by catalytic combustion with oxygen, are avoided in that the localized build-ups of hydrogen that result in the safety tank after a breakdown as a consequence of superimposed atmosphere layers that are in equilibrium with one another are again broken up by effecting in a specific portion of one such atmosphere layer a localized change of the density, for example by introducing into this locally limited atmosphere region a gas having a different density, preferably helium, so that due to the change in density brought about in this manner, this atmosphere layer locally undergoes a vertically directed acceleration that generates a convection.
Unfortunately, this method also has a drawback, namely that in order to be able to carry it out relatively expensive apparatus are required, for example special conduits that must be disposed at different levels and must lead to different areas within the safety tank in order if a breakdown occurs to be able to carry out a precise introduction of the gas or a planned localized change of the temperature in this atmosphere region. Such conduits for the localized changing of the density via the supply of a gas to the pertaining region of the safety tank must communicate with sources of gas, for example an appropriate number of gas tanks in which the gas is under great pressure or exists in a liquid state, with these sources of gas being disposed externally of the safety tank. The ga tanks themselves require special handling and monitoring. Furthermore, a precise monitoring of the atmosphere in the safety tank is necessary in order to be able to detect and break up localized build-ups.
It is therefore an object of the present invention to provide a method that avoids the aforementioned drawbacks of the known methods, is easy to carry out, and above all, in contrast to the known methods described above, right from the beginning avoids the formation of ignitable hydrogen/oxygen mixtures due to build-up in localized regions of the safety tank of a nuclear reactor.
This object, and other objects and advantages of the present invention will appear more clearly from the following specification.